1. Field of the Invention
The present invention relates to a display device, and more particularly, to a liquid crystal display device. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for forming multi-domains in each of the pixels of a liquid crystal display device.
2. Description of the Related Art
One of the types of liquid crystal displays (LCDs) typically used in most recent years is a twisted nematic (TN) mode LCD. The structure of a TN mode LCD includes two substrates on which respective electrodes are formed and a layer of liquid crystal molecules between the two substrates. The liquid crystal molecules within the layer have a long shape oriented parallel to each of the two substrates with a constant pitch, and are spirally twisted. Thus, a liquid crystal director can be oriented when a voltage is applied across the electrodes on the two substrates.
The TN mode LCD has been increasingly used and researched because it provides excellent color reproducibility. However, since light is not completely cut off during the off-state in a TN mode LCD, a contrast ratio is poor. Further the contrast ratio varies with a viewing angle. Accordingly, it is difficult to present a stable image because halftone brightness varies as the viewing angle is varied. In other words, the appearance of an image depends on the angle at which the LCD is viewed.
To address image variation due to different angles of viewing, various types of LCDs have been proposed to present a stable image over a wide range of viewing angles. For example, an in-plane switching mode (IPS) LCD having two electrodes disposed on one plane such that a transverse electric field is generated across the electrodes to reliably cut off light during the off-state has been developed. In another example, a film-compensated mode LCD has been developed in which a compensation film compensates for image variation due to change in the angle in which the LCD is viewed. In yet another example, a vertical alignment (VA) mode LCD has been developed that uses a vertical alignment layer and a negative liquid crystal with a negative dielectric anisotropy to reliably cut off light during the off-state.
The VA mode LCD is mainly classified into a multi-domain vertical alignment (MVA) mode LCD in which a plurality of domains are formed and a liquid crystal direction of each domain is different, and an advanced super-V (ASV) mode LCD in which a pixel electrode is divided into small parts and a liquid crystal direction is controlled by a rib in a central portion of the divided pixel electrode. The MVA mode LCD and the ASV mode LCD are configured such that the liquid crystal directors are opposite to each other to compensate for image variations due to change in the angle in which the LCD is viewed. Therefore, the MVA mode and ASV mode enable the LCD to present a consistent image throughout a wide range of viewing angles.
FIG. 1 is a plan view of the related art MVA mode LCD, and FIG. 2 is a cross-sectional view taken along the line I-I′ of FIG. 1. Referring to FIGS. 1 and 2, the related art MVA mode LCD includes an upper substrate 21, a lower substrate 111 and a layer of liquid crystal molecules interposed therebetween. Herein, the lower substrate 11 includes a gate line 12 and a data line 15, which are respectively arranged in row and column directions, and cross each other so as to define a pixel region. A pixel electrode 17 is formed in the pixel region. A thin film transistor (TFT) is formed in adjacent to a crossing of the gate line 12 and the data line 15, and a plurality of first electric field distortion units 33 is formed in a predetermined region of the pixel electrode 17 for controlling a liquid crystal director through electric field distortion. The TFT is selectively switched by a scan signal of the gate line 12 so as to apply a data signal of the data line 15 to the pixel electrode 17.
As shown in FIG. 1, the first electric field distortion unit 33 has the shape of a slit, which is formed by selectively removing a portion of the pixel electrode 17. Meanwhile, the TFT is configured with a gate electrode 12a extending from the gate line 12, a gate insulating layer 16 on the gate electrode, a semiconductor layer 18 formed on the gate electrode in a shape of an island, source/drain electrodes 19 and 15a that extend from the data line 15, and the pixel electrode 17.
Although not illustrated in FIGS. 1 and 2, the lower substrate 11 further includes a storage capacitor parallel to the gate line 12. The storage capacitor maintains a charged voltage in the liquid crystal layer while the TFT is turned off so that it prevents image quality from deteriorating.
The upper substrate 21 includes a black matrix 22 for preventing light leakage, a color filter layer 23 of red, green and blue formed between the black matrix layers 22 for displaying a color on a screen, a common electrode 24 stacked on the color filter layer 23 such that it is opposite to the pixel electrode 17 of the lower substrate 11, a plurality of second electric field distortion units 31 formed in a predetermined region of the common electrode 24 for controlling the liquid crystal director by the electric field distortion. Although it is illustrated in FIG. 1 that the second electric field distortion unit 31 has the shape of a rib, which is formed by separately depositing a dielectric material on the common electrode 24 followed by patterning a conductive material, the second electric field distortion unit 31 may be formed in a shape of a slit within the conductive material like the first electric field distortion unit 33.
As shown in FIG. 1, the first and second electric field distortion units 33 and 31 are alternately arranged in the shape of oblique lines which are parallel to each other, to thereby form multi-domains. However, in case of the related art VA mode LCD, it is necessary to perform a deposition process of a dielectric material on the upper substrate 21 as well as patterning processes to pattern an ITO electrode to form the second electric field distortion unit 31 in the shape of a rib or slit, as shown in FIG. 2. Therefore, there is a drawback in that the number of the process inevitably increases the implementation of multi-domains in each pixel region.